When loading bulk material, such as coal or grain, into the hold of a ship, the bulk material is normally carried by a belt conveyor to a position above the hold to be filled, and then discharged under gravity into the hold. There are several problems associated with this basic loading method. First, the falling material generates a considerable amount of dust, posing health risks and fouling the environment. The fall from the conveyor into the hold is also likely to degrade the product, and cause unwanted aeration. The impact of the material on parts of the ship or other equipment accelerates abrasive wear of such parts of equipment.
Various types of bulk materials handling equipment have been developed in order to reduce one or more of the abovementioned problems. One device, sold under the trade name CHOKEFEEDER, attempts to minimise dust generation during loading by discharging the product into a spout at the end of the belt conveyor, and "choking" off or sealing the bottom of the spout by a set of vanes which are either fully opened or closed. Material is fed continuously into the top of the spout and freefalls down the spout. When the product builds up to a predetermined height, the vanes are opened fully to discharge the product. When the product level in the spout falls to a level near the bottom, the vanes are closed until the product builds up to the upper limit again.
Although this device reduces dust generation, it still allows the product to free fall, on average, an appreciable distance (which can be up to the full height of the spout). The product gains speed and tends to segregate while free-falling. Its movement is then halted abruptly as it impacts against the stationary product at the base before being forced through the discharge control valves. The operation involves repeated filling and emptying of the spout.
The upper and lower product operating heights of the CHOKEFEEDER can be varied for different products. When loading fragile materials, such as petroleum coke, the control system varies the discharge vane opening and closing times to keep the working range of the product closer to the upper end of the spout to limit the distance that the product falls. Since the vanes are either fully open or fully shut, the product is still subjected to the repetitive starting and stopping motion which results in product degradation and some dust generation. Further, as the vanes open and close frequently under load, large inertia forces are generated as the column of material stops and starts suddenly.
Another known method of material transfer uses a series of hoppers or cones. Material cascades from one cone to the next down the length of the feeder. The design tries to limit the maximum velocity achieved by the material in the spout. However, this method still results in the product accelerating and decelerating from one cone to the next.
It is an object of the present invention to provide an improved materials handling system which overcomes or ameliorates at least some of the abovedescribed problems, or which at least provides a useful alternative.